Inspired by the successfully experimental synthesis of Janus structures recently, we systematically study the electronic, optical, and electronic transport properties of Janus monolayers In2XY (X/Y = S, Se, Te with X № Y) in the presence of a biaxial strain and electric field using density functional theory. Monolayers In2XY are dynamically and thermally stable at room temperature. At equilibrium, both In2STe and In2SeTe are direct semiconductors while In2SSe exhibits an indirect semiconducting behavior. The strain significantly alters the electronic structure of In2XY and their photocatalytic activity. Besides, the indirect-direct gap transitions can be found due to applied strain. The effect of the electric field on optical properties of In2XY is negligible. Meanwhile, the optical absorbance intensity of the Janus In2XY monolayers is remarkably increased by compressive strain. Also, In2XY monolayers exhibit very low lattice thermal conductivities resulting in a high figure of merit ZT, which makes them potential candidates for room-temperature thermoelectric materials.

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Since the recent successful experimental synthesis of MoSi2N4 [Science, 369 (2020), 670], the “MA2Z4 family” has been of particular interest to the scientists in the field of materials science due to its outstanding physical properties. In this paper, the first‐principles calculations are performed to study the structural, elastic, and electronic properties of novel two‐dimensional (2D) Janus MSiGeN4 monolayers (M = Ti, Zr, Hf). The calculations of phonon spectra indicate that monolayers MSiGeN4 are dynamically stable and can be experimentally synthesized. The obtained Young's modulus and Poisson's ratio of the Janus structures MSiGeN4 are much larger than that of other binary 2D materials and meet the mechanical stability criteria suggested by Born and Huang. In the calculations using either PBE or HSE06 functionals, the Janus MSiGeN4 structures exhibit indirect semiconductor characteristics with larger band gaps than that of similar septuple‐atomic‐layer materials, such as MoSiGeN4 and WSiGeN4. In addition, the influences of biaxial strain and external electric field on the electronic structure of MSiGeN4 are investigated. It is found that the biaxial strain tunes the electronic characteristics more significantly than the external electric field. The obtained results can provide insights into novel Janus monolayers with potential applications in electronic devices.

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